Many electronic devices such as dynamic random access memory (DRAM) cells and transistor gates include charge storage capacitors coupled to an access device, such as a Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET). In particular, a MOSFET can apply or remove electric charge on a capacitor thus affecting a logical state defined by the stored charge. Many electronic devices require materials with high dielectric constant (“k”) values (or dielectric tensor values) to effectively store electric charge.
The dielectric constant value of a material may be defined as the ratio of its absolute permittivity tensor, c, to the permittivity of vacuum, ∈o, (i.e., k=∈/∈o). The dielectric constant is unitless because it is a ratio of two similar quantities.
Conventional capacitors include two conductors, such as parallel metal or polysilicon plates, which function as electrodes. These electrodes are insulated from each other by an interposed dielectric material. For example, one type of capacitor used in DRAM cells is a metal-insulator-metal (MIM) capacitor.
Materials having a rutile crystal structure, such as the rutile polymorph of titanium dioxide (TiO2), have been used as dielectric materials for high-κ dielectric applications. TiO2-based dielectric materials have the potential to exhibit relatively high dielectric constant values. However, the effective dielectric constant, keff, typically remains below 100.0 (e.g., 80-90) due to conventional semiconductor manufacturing sequence(s).
Particularly, high dielectric constant values have been discovered for TiO2 single crystals when measured along a tetragonal axis (i.e. along the [001] crystal direction). For example, some single crystal rutile TiO2 materials have been found to exhibit dielectric constant values of 86 (κ⊥) and 170 (κ∥).
As such, the effective dielectric constant values exhibited in semiconductor-based capacitive devices suggest that for a typical modern semiconductor manufacturing sequence, the materials crystallize in a manner such that the effective dielectric constant is reflected by the lower dielectric constant κ⊥ value. Most notably, the lower dielectric constant κ⊥ values are typical for conventional thin film deposition techniques utilized to deposit the dielectric film parallel to the electrode(s) within the trenches. Because the dielectric film is likely grown with a (110) free surface, thus having the high-k [001] direction in-plane, the direction normal to the electrodes will be the low-k direction, thereby leading to dielectric constant values of 86 (or lower due to structural defects) in case of TiO2.
At best, a polycrystalline film having a rutile crystal structure having randomly oriented crystallites may be utilized. In this scenario, the effective dielectric constant value, κeff, is an average of κ⊥ and κ∥ with a twice larger weight given to the smaller dielectric constant κ⊥ value.
As such, what is needed is a method to increase the effective dielectric constant values of dielectric materials within semiconductor-based capacitive devices. The present disclosure addresses such a need.